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2.
R. Chitra Pascal Roussel R. R. Choudhury 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(9):o547-o549
The title complex, 2CH4N2S·C4H6O4, is a host–guest system. The asymmetric unit consists of one complete thiourea molecule and one‐half of a dimethyl oxalate molecule lying on an inversion centre. The host thiourea molecules are connected to form zigzag chains by N—H⋯S hydrogen bonds. The guest dimethyl oxalate molecules provide O‐atom acceptors for N—H⋯O hydrogen bonds, thus interconnecting the chains of thiourea molecules to form completely connected sheets. The reduction in temperature from 300 to 100 K leaves the structure unchanged and still isostructural with that previously determined for the analogous thiourea–diethyl oxalate (2/1) complex. It does, however, induce closer packing of the molecules, general shrinkage of the unit cell and shortening of the hydrogen bonds, these last two to the extent of 1–2%. 相似文献
3.
Pascal Ferraro Christophe Godin 《Journal of Algorithms in Cognition, Informatics and Logic》2003,48(2):385-406
In this paper we consider the problem of finding a minimum cost mapping between two unordered trees which induces a graph with a minimum number of connected components. The proposed algorithm is based on the generalization of an algorithm for computing an edit distance between trees, and it solves the stated problem in sequential time precisely in O(|T1|×|T2|×(degT1+degT2)×log2(degT1+degT2)). 相似文献
4.
A preconditioning approach based on the artificial compressibility formulation is extended to solve the governing equations for unsteady turbulent reactive flows with heat release, at low Mach numbers, on an unstructured hybrid grid context. Premixed reactants are considered and a flamelet approach for combustion modelling is adopted using a continuous quenched mean reaction rate. An overlapped cell‐vertex finite volume method is adopted as a discretisation scheme. Artificial dissipation terms for hybrid grids are explicitly added to ensure a stable, discretised set of equations. A second‐order, explicit, hybrid Runge–Kutta scheme is applied for the time marching in pseudo‐time. A time derivative of the dependent variable is added to recover the time accuracy of the preconditioned set of equations. This derivative is discretised by an implicit, second‐order scheme. The resulting scheme is applied to the calculation of an infinite planar (one‐dimensional) turbulent premixed flame propagating freely in reactants whose turbulence is supposed to be frozen, homogeneous and isotropic. The accuracy of the results obtained with the proposed method proves to be excellent when compared to the data available in the literature. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
5.
The projective method for solving linear matrix inequalities 总被引:2,自引:0,他引:2
Numerous problems in control and systems theory can be formulated in terms of linear matrix inequalities (LMI). Since solving
an LMI amounts to a convex optimization problem, such formulations are known to be numerically tractable. However, the interest
in LMI-based design techniques has really surged with the introduction of efficient interior-point methods for solving LMIs
with a polynomial-time complexity. This paper describes one particular method called the Projective Method. Simple geometrical
arguments are used to clarify the strategy and convergence mechanism of the Projective algorithm. A complexity analysis is
provided, and applications to two generic LMI problems (feasibility and linear objective minimization) are discussed. 相似文献
6.
We study experimentally and theoretically two polarization effects in a vertical cavity surface emitting laser submitted to optical feedback. In a first experiment, we obtain flips between two linearly polarized laser modes up to a frequency of 50 MHz using an external cavity with a polarizer. In a second experiment, polarization self modulation is demonstrated up to a frequency of 2.6 GHz, using a quarter wave plate instead. Numerical calculations, based on a four levels model for the active medium, show a good agreement with the experiments. 相似文献
7.
A new method is presented to analyze reflection losses of integrated mirrors, taking into account the exact guided mode profile and assuming that this profile remains unchanged up to the reflecting plane. The fraction of the reflected light coupled to one of the guided modes of the output waveguide is calculated, taking into account the mirror reflection coefficient. The influence of both translation and tilt of the reflecting plane is investigated. The method applies for every guided mode and any reflection angles. Numerical calculations are derived for a 90° optical corner mirror 相似文献
8.
Pascal Cherrier 《Bulletin des Sciences Mathématiques》2007,131(4):375-396
We study a parabolic version of a system of Von Karman type on a compact Kähler manifold of arbitrary dimension. We provide local in time regular solutions, which can be extended to global bounded ones if the data of the problem are small. 相似文献
9.
10.
An efficient preconditioner is developed for solving the Helmholtz problem in both high and low frequency (wavenumber) regimes. The preconditioner is based on hierarchical unknowns on nested grids, known as incremental unknowns (IU). The motivation for the IU preconditioner is provided by an eigenvalue analysis of a simplified Helmholtz problem. The performance of our preconditioner is tested on the iterative solution of two‐dimensional electromagnetic scattering problems. When compared with other well‐known methods, our technique is shown to often provide a better numerical efficacy and, most importantly, to be more robust. Moreover, for the best performance, the number of IU levels used in the preconditioner should be designed for the coarsest grid to have roughly two points per linear wavelength. This result is consistent with the conventional sampling criteria for wave phenomena in contrast with existing IU applications for solving the Laplace/Poisson problem, where the coarsest grid comprises just one interior point. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007 相似文献